1. Field of the Invention
The present invention relates to digital image processing methods and more particularly to improved methods for image rotation.
2. Description of the Prior Art
The following are systems representative of the prior art.
U.S. Pat. No. 4,627,020 teaches a method for rotating image data which recognizes and takes advantage of the fact that large areas of most images are background color such as white and that digital representations of the pels in these background areas need not be rotated since an all zeros 8.times.8 bit block of pels is the same in any 90 degree rotation of the block. However, the patent does not teach nor suggest the simplified method for rotation of n X n bit blocks including transposing bits within the block and flipping the block according to the present invention.
U.S. Pat. No. 3,976,982 shows a method of rotation of an image by 90 degree among other functions performed. However, the patent does not show a method for rotating an image by 90 degrees which includes rotation of n X n bit blocks including transposing bits within the block and flipping the block.
U.S. Pat. No. 3,968,475 shows a digital processor for extracting data from a binary image in which the image is divided into an array of sample areas each sample area containing an array of binary data spaces. Although the patent demonstrates image rotation by any one of a number of predetermined angles, the patent does not show a method for rotating an image by 90 degrees either clockwise or counterclockwise including rotation of n X n bit blocks including transposing bits within the block and flipping the block.
U.S. Pat. No. 4,052,699 relates to an image processing system wherein video data is stored in a matrix having n rows and n columns. The image is rotated 90 degrees in a piece-meal fashion by vertically accessing word by word video data previously stored as horizontal words. However, the method and apparatus of the patent do not include rotation of n X n bit blocks including transposing bits within the block and flipping the block.
U.S. Pat. No. 4,168,488 shows hardware for image rotation of a word organized image buffer where the buffer is divided into a number of square sections each storing a portion of the full image. Although the patent shows apparatus for image rotation through an angle of 90 degrees, the patent does not show a method which includes rotation of n X n bit blocks including transposing bits within the block and flipping the block.
U.S. Pat. No. 4,225,929 relates to a code converter including means for rotating an image about a center point. The patent does not include rotation of n X n bit blocks including transposing bits within the block and flipping the block.
U.S. Pat. No. 4,271,476 relates to apparatus for rotating horizontal scan format images into vertical scan format images for printing or other processing. The patented apparatus divides the image into a number of sections and then rotates each section in sequence. The patent does not show a method including rotation of n X n bit blocks including transposing bits within the block and flipping the block.
U.S. Pat. No. 4,467,448 relates to an image rotation control circuit for controlling printing of an image on a printer. The published control circuit does not store the entire display but merely a single line at a time which is converted from a horizontal line to a vertical line or vice versa for printing. The publication does not show a method for rotating an image by 90 degrees including rotation of n X n bit blocks including transposing bits within the block and flipping the block.
An article in the IBM Technical Disclosure Bulletin, Vol. 18, No. 8, January 1976, p. 2640 shows a method for rotation of images using contour compressed data. However, the article does not include rotation of n X n bit blocks including transposing bits within the block and flipping the block.
An article in the IBM Technical Disclosure Bulletin, Vol. 13, No. 11, April 1971, p. 3267 shows a method for performing a fast transformation of axes on two dimensional binary images. The artcile does not include rotation of n X n bit blocks including transposing bits within the block and flipping the block.
An article in the IBM Technical Disclosure Bulletin, Vol. 18, No. 8, January 1976 at page 2633 shows a shift register system for image orientation which among other functions rotates an image in 4.times.4 array of characters. The articles does not include rotation of n X n bit blocks including transposing bits within the block and flipping the block.
A letter by J.O. Eklundh entitled "A Fast Computer Method for Matrix Transposing." in the IEEE Transactions on Computers, July 1972 at Page 801, presents a method for transporting n X n data matrices having some similarity to the transposition algorithm used with the method of the present invention. However, the article does not show a method for rotation of n X n bit blocks including transposing bits within the block and flipping the block.
The prior art discussed above does not teach nor suggest the present invention as disclosed and claimed herein.